The word "risk" is not only a popular everyday term but also an important scientific term. Although there is no uniform and strict definition of it in the world at present, the core of various viewpoints is basically the same. Summarizing the definitions of risks by authoritative figures and institutions at home and abroad, we have the following views [109,110,214, 186 ~ 206]:

(1) In Weber's dictionary, "risk is the possibility of facing injury or loss".

(2) Wilson and others published a paper in the international authoritative scientific journal Science on 1987, describing the nature of risk as "uncertainty" and defining it as "expected value".

(3) Smith (1996) defined "risk is the probability of disaster".

(4) Mascre (1989) defines "risk is the loss caused by accidents".

(5)Tobin and Montz( 1997) define that "risk is the product of the probability of disaster and expected loss".

(6) Dele (1998) is defined as "risk is the combination of the probability of an accident and the scale of the consequences".

(7) Hurst (1998) is defined as "risk is a description of the probability and result of an accident".

(8) The definition published by the United Nations Department of Humanitarian Affairs is that "risk is the possibility of a disaster in a certain area and within a certain period of time and the expected loss of life, property and economic activities caused by it".

The author believes that if landslides may occur in deserted places, it will not cause casualties or property losses. Obviously, the risk of landslide accident is zero. So the above three definitions of "risk is the probability of an accident" are inaccurate. If you think that "risk is the loss caused by the accident", it is only an after-the-fact loss assessment and cannot be called "risk". Therefore, the definition of risk in Maskrey( 1989) is not comprehensive.

The above definitions (5) to (8) combine the possibility of an accident with the possible losses after the accident, which is more reasonable. Therefore, the author agrees with the definition published by the United Nations Department of Humanitarian Affairs, that is, "risk refers to the possibility of a disaster in a certain region and within a certain period of time and the expected loss of life, property and economic activities caused by it".

Second, the expression of risk.

If "risk degree" is used to represent risk, according to the conditions and laws of geological environmental accidents and the author's experience, geological environmental risk can be summarized as the following three mathematical expressions:

(1) Risk = accident probability × losses caused. The author thinks that the advantage of this calculation is that different risks can be compared, and it is suitable for geological environment accident risks that can be calculated or predicted by probability.

(2) Risk = accident risk × losses caused. The "degree of danger or danger" here is a noun with no meaning of injury or loss, which is equivalent to the "susceptibility" of environmental accidents. The author thinks that the probability of many accidents (such as collapse, landslide, debris flow, ground collapse, ground fissure, etc.) cannot be calculated or predicted. ), but the risk (degree) can only be evaluated according to professional knowledge and geological conditions. Therefore, this kind of risk can be expressed by "risk degree = accident risk degree × loss caused", and the result can also be used to compare risks.

(3) Risk = the combination of the possibility of an accident and the losses caused. The author believes that it is very cautious to simply express or even calculate risks, especially those caused by accidents such as geological disasters or environmental geological problems, and compare them with the results. If the probability of landslide A and landslide B and A is 0.5%, the possible economic loss will be 65.438+0 billion yuan and the casualties will be 65.438+0 million. The probability of B occurrence is 50%, and the possible economic loss after B occurrence is 6.5438+0 million yuan, with 654.38+0 casualties. The risks of A and B are 500,000 losses and 5 casualties. Can we say that the risks are the same? I'm afraid it's hard to say (because 0.5% is not a small probability event). Therefore, it may be an effective method to express the geological environment risk by "risk degree = the sum of the possibility of accidents and the losses caused". The "possibility of accident" here can be calculated as "probability" or "accident risk"

Therefore, according to the occurrence and harmfulness of geological disasters and environmental geological accidents, the author prefers to use "risk degree = combination of accident possibility and harmfulness" to describe geological environmental risks.

Third, the basic idea of geological environment risk assessment

Geological environmental risk is a concept composed of the possibility P of geological environmental accidents and the damage they will cause. Assume that the probability of geological environment accidents (with the meaning of probability or danger) is p (x); The loss or injury caused by the accident is called "risk consequence" D(x), and the risk can be characterized as follows

Economic evaluation of urban geological environment risk

In the formula (8- 1- 1), x is a specific event or accident. Generally speaking, an actual environmental accident is composed of several independent events, so the risk R(x) of this environmental accident is

Economic evaluation of urban geological environment risk

or

Economic evaluation of urban geological environment risk

or

Economic evaluation of urban geological environment risk

Therefore, the task of geological environmental risk assessment is to find out its R(x) (that is, P(x), D(x)).

According to the above two formulas, it is a classic basic method to calculate the probability or danger (degree) P(x) of a risk accident and its possible harm or loss D(x), and then calculate the risk R(x). This is the basic idea of geological environment risk assessment.

Four, the basic content and technical route

1. Basic content

The contents of urban geological environment risk assessment are numerous and complicated, as shown in Figure 8- 1- 1.

2. Technical route

The technical route of urban geological environment risk assessment is shown in Figure 8- 1-2.